Influence of ultrasonic surface rolling process on surface characteristics and micro-mechanical properties of uranium

Ultrasonic surface rolling process (USRP) is a novel surface modification technique based on surface severe plastic deformation (SSPD). The present study aims to investigate the surface characteristics and micro-mechanical properties of uranium by USRP treatment. By means of theoretical calculations and experimental tests, it was concluded that the USRP treated specimen showed a smoother and more densified surface. The surface roughness Rv, Rp and Ra were reduced to 0.590 μm, 0.669 μm and 0.249 μm, respectively. Meanwhile, the U(002) basal texture and stronger residual compressive stresses were presented on the surface. The gradient microstructure including severe deformation layer and deformation twinning layer was generated after USRP treatment. Furthermore, there was a typical gradient strength distribution with significantly higher values on the top surface, followed by a gradual decrease until the matrix was reached. As a result, the improvement of surface strength was achieved and the ductility of matrix in core was maintained. These improvements in the micro-mechanical properties were attributed to the results of surface integrality, orientation of grains, residual compressive stress, severe deformation layer and deformation twinning layer. However, excessive passes of USRP treatment led to the nucleation and propagation of surface cracks and the release of residual compressive stress, which were not conducive to the improvement of micro-mechanical properties.